I have one FutureBuilderthat has a basic structure.

FutureBuilder(
      future: api.sincronizacion(),
      builder: (BuildContext context, AsyncSnapshot<List> snapshot) {
         ...
      })

The problem that I present is that for some strange reason it executes the method at least 2 times sincronizacion(), this causes me to generate errors with some other methods such as insertions to the database with the same one idthat PRIMARY KEYgenerates an exception.

One of the exceptions is received.

SqfliteDatabaseException (DatabaseException(UNIQUE constraint failed: versions._id (code 1555 SQLITE_CONSTRAINT_PRIMARYKEY[1555])) sql 'INSERT INTO versions (_id, stability, majorversion, minorversion, revision) VALUES (?, ?, ?, ?, ?)' args [5dc08909cad9c242119da306, beta, 1, 0, 12]})

Another exception that occurs

Exception has occurred. SqfliteDatabaseException (DatabaseException(database_closed 1))

Simple Example

This example simulates the simple execution of what I think is the problem with Futureusing a variable numberto count the number of times the method is called without restarting the instance.

At the end of the load in data it returns 3,2 and on one occasion 4 which should only be 1 because only 1 call to the method _getDatathat increases is expectednumber

main.dart

void main() => runApp(MyMaterialApp());

class MyMaterialApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    print('Ejecutando MyMaterialApp');
    return MaterialApp(
      home: SplashLoad(),
    );
  }
}

class SplashLoad extends StatefulWidget {

  @override
  _SplashLoadState createState() => _SplashLoadState();
}

class _SplashLoadState extends State<SplashLoad> {
  final apiSimulation = new ApiSimulation();

  @override
  Widget build(BuildContext context) {
    print('SplashScreen');
    return Scaffold(
      body: Container(
        child: Center(
          child: FutureBuilder(
            future: apiSimulation.sincronizacion(),
            // initialData: InitialData,
            builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
              if (snapshot.hasData) {
                return Text('Carga completa data:${snapshot.data}');
              }
              return CircularProgressIndicator();
            },
          ),
        ),
      ),
    );
  }
}

ApiSimulation

it simulates a bit what it would be like to call about 4 seconds to get data from a server and add it to a database.

class ApiSimulation {
  int number = 0;
  Future<int> sincronizacion()async{
    print('INICIANDO SINCRONIZACIÓN');
    await Future.delayed(Duration(seconds: 2));
    final data = await _getData();
    return data;
  }

  Future<int> _getData() async{
    number++;
    print('ejecutando getData$number');
    await Future.delayed(Duration(seconds: 2));
    return number;
  }
}

Result in console

I/flutter (32404): Ejecutando MyMaterialApp
I/flutter (32404): SplashScreen
I/flutter (32404): INICIANDO SINCRONIZACIÓN
I/flutter (32404): Ejecutando MyMaterialApp
I/flutter (32404): SplashScreen
I/flutter (32404): INICIANDO SINCRONIZACIÓN
I/flutter (32404): ejecutando getData1
I/flutter (32404): ejecutando getData2

end of example

I have done multiple tests

• Follow the execution of the code line by line with the VisualStudioCode tool
• Changing the method implementation from static Future<List> sincronizacion() async {...to Future<List> sincronizacion() async {just in case helps
• Modify my mainthinking that the way the interface was called would cause it to be called 2 times and that at the same time execute againsincronizacion()
  • Previously

    MaterialApp(
        localizationsDelegates: [CustomLocalizationDelegate()],
        routes: getApplicationRoutes(),
        home: MyApp(),
        ...
    

  • After where getApplicationRoutes()contains MyApp()in the path'/'

    MaterialApp(
        localizationsDelegates: [CustomLocalizationDelegate()],
        routes: getApplicationRoutes(),
        initialRoute: '/',
        ...
    

The following classes and methods are from my project that exhibits the problem.

main

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final auth = Auth();
  final prefs = new PreferenciasApp(); //singleton
  await prefs.initPrefs();

  runApp(Provider(
    auth: auth,
    child: MaterialApp(
      localizationsDelegates: [CustomLocalizationDelegate()],
      routes: getApplicationRoutes(),
      initialRoute: '/',
      theme: ThemeData(...),
    ),
  ));
}

getApplicationRoutes() in routes.dart file

// imports
...

final main = MyApp();
final home = Home(selectBottom: 0,);
final registro = Registro();
final inicioSesion = InicioSesionPlussUltraPower();
final playlist = PlaylisPage();
final inicio = Inicio();
final detallePlay = DetallePlay();

Map<String, WidgetBuilder> getApplicationRoutes() {    
  return <String, WidgetBuilder>{
    "/"           : (BuildContext context) => main,
    "/Himnario"           : (BuildContext context) => home,
    "/Registro"           : (BuildContext context) => registro,
    "/Inicio de sesión"   : (BuildContext context) => inicioSesion,
    "/PlayList"           : (BuildContext context) => playlist,
    "/Inicio"             : (BuildContext context) => inicio,
    DetallePlay.routeName : (BuildContext context) => detallePlay,
  };
}

My App

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final prefs = new PreferenciasApp();
  final api = new ApiService();
  @override
  Widget build(BuildContext context) {
    print('Ejecutando myApp------------------------->>>>>');
    
    return FutureBuilder(
      future: api.sincronizacion(),
      builder: (BuildContext context, AsyncSnapshot<List> snapshot) {
        if (snapshot.hasData) {
          final result = snapshot.data;

          if (result[0] == null) {
            return Container(...),
            );

          } else {
            text = result[0] ? 'Carga completa' : 'Error en la carga.';
            var page = prefs.idUser.isEmpty ? Inicio() : InicioSesion();
            return SplashScreen(
               seconds: 1,
               navigateAfterSeconds: page,
               ...
            );
          }
        } //snapshot.hasData

        return Container(...);
      },
    ); // FutureBuilder
  }
}